Can we have multiple 1-wire devices on single pin?

[CuriousOne]

I want to use PIC16F1503 and have to chain thermometers due to pin count. I guess, running above, complex code might not be possible on this wimpy chip?

The task is as follows:
There are 3 fans with PWM input and tachometer output, MAX7219 display and array of buttons. Circuit will monitor fan rpm and adjust it according to individual thermometer reading.

I have 12 IO pins on that chip, I'm thinking about allocating them in the following way:
3 pins - hardware PWM outputs.
3 pins - tachometer inputs.
3 pins - driving MAX7219
1 pin (MCLR), used as ADCIN, to attach several buttons.
1 pin - relay driver, for emergency shutdown.

So I have only 1 pin, for attaching 3 DS18B20....

[Dave]

So... Do it....

[pedja089]

I want to use PIC16F1503 and have to chain thermometers due to pin count. I guess, running above, complex code might not be possible on this wimpy chip?

You can read address, without searching, if it is only one device present at bus. Just write command $33, and collect next 64bit. Do this 3 time, one for each sensor.
Connect all DS to bus.
Write $CC,$44 to start temperature conversion on all DS simultaneously.
Then use match ROM($55) followed by address, to read data from one DS.
Look at page 11 in this datasheet https://datasheets.maximintegrated.c...ds/DS18B20.pdf

[CuriousOne]

I have an idea, fan tachometer output will be tied to VDD via 4.7k resistor, as DS18B20 should be. Fan outputs pulses not so fast, so what if I attach DS18B20 to same pin as fan tachometer output? and say, after falling edge of tachometer pulse, perform all DS18B20 stuff, while fan pulls pin high again?

[Dave]

I believe it takes ~750 Ms. to complete 1 conversion. With that being said, How are you going to discern if the next pulse is the tach output or the DS output?

[CuriousOne]

Yes, so I came to different solution. I also have PWM output pin, which goes into fan PWM in. So I'll hook DS18B20 to it - When I need to use thermometer, I will stop HPWM output on that pin, read the thermometer and then resume HPWM operation. I guess, fan will have enough inertia to have no significant impact on it's rpm.

[towlerg]

You do realize 750ms is three quarters of a second? Fan speed will be very wobbly.

[CuriousOne]

Fan won't stop in absence of PWM signal. most fans, without PWM signal applied, will default to 30-50% RPM.